A human eye can suffer diseases that impair a patient's vision. For instance, a cataract may increase the opacity of the lens, causing blindness. To restore the patient's vision, the diseased lens may be surgically removed and replaced with an artificial lens, known as an intraocular lens, or IOL. In other cases, glaucoma may result in a gradual and undesirable increase of intraocular pressure (IOP). In such instances, a shunt may be implanted to help control pressure within the eye. In either case, it is generally desirable to maintain the ocular device at a fixed location within the eye.
The simplest IOLs are monofocal IOLs that are fixed within the eye and have a single focal length or power. Unlike the eye's natural lens, which can adjust its focal length within a particular range in a process known as accommodation, these IOLs cannot generally accommodate. As a result, objects at a particular position away from the eye appear in focus, while objects at increasing distances away from that position appear increasingly blurred. Bifocal or multifocal IOLs, which are also generally fixed within the eye, produce two or more foci in order to simulate the accommodation produced by the eye's natural lens. For example, one of the foci may be selected to provide distant vision, while a second focus is selected to provide near vision. While multifocal IOLs improve the ability of a subject to focus on objects over a range of distances, the presence of more than one focus generally results in reduced contrast sensitivity compared to monofocal IOLs.
An IOL may also be used for presbyopic lens exchange. Presbyopia is the condition where the eye exhibits a progressively diminished ability to focus on objects over a range of distances. It is caused by a gradual loss of “accommodation” in the natural lens inside the eye due to age-related changes that make the lens harder and less elastic with the years.
An improvement over the fixed IOLs (either monofocal or multifocal) is an accommodating IOL, or aIOL, which can adjust its power and/or axial position within a particular range. As a result, the patient can clearly focus on objects over a range of distances from the eye in a way that is similar to that provided by the natural lens. This ability to accommodate may be of tremendous benefit for the patient, and more closely approximates the patient's natural vision than monofocal or multifocal IOLs. Such artificial implantable lenses can take the form of injectable IOLs (polymer material injected into the capsular bag), Deformable IOLs (the lens' optic shape change creates optical power change), axially moving IOLs, Dual Optics IOLs, etc, or some combination thereof. Alignment of aIOLs within the eye may be particularly important. Thus, reliable attachment means may be especially useful in assuring quality optical performance for aIOLs.
The human eye contains a structure known as the capsular bag, which surrounds the natural lens. The capsular bag is transparent, and serves to hold the lens. In the natural eye, accommodation is initiated in part by the ciliary muscle and a series of zonular fibers, also known as zonules. The zonules are located in a relatively thick band mostly around the equator of the lens, and impart a largely radial force to the capsular bag that can alter the shape and/or the location of the natural lens and thereby change its effective power and/or focal distance.
In a typical surgery in which the natural lens is removed from the eye, the lens material is typically broken up and vacuumed out of the eye, but the capsular bag is left generally intact. The remaining capsular bag is extremely useful in that it may be used to house an aIOL, which is acted on by the zonules to change shape and/or shift in some manner to affect the lens power and/or the axial location of the image.
The aIOL has an optic, which refracts light that passes through it and forms an image on the retina, and may also include a haptic, which mechanically couples the optic to the capsular bag or holds the aIOL in contact with the capsular bag. During accommodation, the zonules exert a force on the capsular bag, which in turn exerts a force on the optic. The force may be transmitted from the capsular bag directly to the optic, or from the capsular bag through a haptic to the optic. In either case, the lens changes shape and/or position dynamically to keep an object in focus on the retina as its distance from the eye varies.
Desirably, the design of the aIOLs effectively translates the ocular forces of the natural accommodative mechanism of the eye [ciliary muscle—zonules—capsular bag] to maximize accommodation amplitude or range. Also, aIOLs may take into account the problem of lens epithelial cell (LECs) proliferation which can cause opacification and stiffening of the capsular bag over time. This phenomenon is caused by the wound healing reactions of the natural lens epithelial cells that remain on the inside of the capsular bag, often in the narrow ring around the equatorial region. Several methods to prevent the LECs from proliferating have been tried, including removing the LECs as much as possible, mechanically as well as pharmaceutically. Alternatively, design features such as a square edge and spacers have been incorporated into the aIOLs.
As mentioned above, ocular implants may also be used in long-term glaucoma treatment. Glaucoma is a progressive disease of the eye characterized by a gradual increase of intraocular pressure (IOP). This increase in pressure is most commonly caused by stenosis or blockage of the aqueous outflow channel, resulting in excessive buildup of aqueous fluid within the eye. The implant solution typically involves suturing a small plate to the sclera in the anterior segment of the eye at the limbus, and inserting a drainage tube into the anterior chamber of the eye, which may also be secured via a suture to the sclera. Once implanted, the body forms scar tissue around the plate. Aqueous humor flow through the tube causes the tissues above the plate to lift and form a bleb. A bleb is a fluid filled space surrounded by scar tissue, somewhat akin to a blister. The fluid within the bleb then flows through the scar tissue at a rate which desirably regulates IOP. More recently, U.S. Pat. Nos. 5,476,445 and 6,050,970 to Dr. George Baerveldt, et al. disclose glaucoma implants or shunts featuring a flexible plate that attaches to the sclera and a drainage tube positioned for insertion into the anterior chamber of the eye. This type of shunt is sold under the tradename Baerveldt® BG Series of glaucoma implants by Advanced Medical Optics (AMO) of Santa Ana, Calif. The Baerveldt® device has an open tube without flow restricting elements. Temporary sutures are used to restrict fluid flow for a predetermined period, after which the bleb forms and fluid drainage is properly regulated. The temporary sutures are either biodegradable or removed in a separate procedure. This method works well, but the timing of suture dissolution is necessarily inexact, and a second procedure undesirable.
In these and other situations, ocular devices and methods are needed for securely attaching ocular implants in an eye. In some instances, reversal of the attachment means is desirable, for example, to allow the device to be more readily explanted. In addition, there exists a need for an aIOL with increased efficiency in converting an ocular force to a change in power and/or a change in axial location of the image, preferably in a way which also reduces the problem of lens epithelial cell proliferation. There is also a need for an alternative to suturing glaucoma shunts in place.